The RC (resistance and capacitance) time constant of a capacitor is indicative of the time it takes to charge or discharge the capacitor. For a given resistance, increasing capacitance will accordingly increase charging/discharging time. However, high cell capacitance becomes more desirable as devices become smaller. The increased RC time constant of high cell capacitance parts may prevent such parts from passing write time sensitive tests, resulting in decreased process margin. Also, tests designed to guardband write speed to the capacitor are limited when high cell capacitance parts are used.
As may be appreciated, improved capacitor constructions and methods of forming them are desired to decrease the RC time constant.